Brake systems for railway car double axle wheel trucks generally include brake shoes mounted on opposite ends of a pair of brake beams which are positioned between the axles. These brake beams are movable away from each other in order to bring such brake shoes into engagement with the wheel treads.
Customarily, these prior art type brake systems include a cylinder and piston for actuating the brake shoes into frictional engagement with the wheels. The cylinder and piston can either be mounted on the railroad car which the wheel truck supports, “car mounted”, or can be mounted on the wheel truck, “truck mounted.” In both cases, a multiple lever system interconnects the piston and the brake beams for proper operation of the brakes.
As is well known in the railway industry, one of the major problems arising in all railway car brake systems is that the load imposed by the cars on their respective wheel trucks can vary considerably from car to car and truck to truck. Thus, in a single train consist, some of the cars may be fully loaded, some partially loaded, and some empty. Conditions may exist where one end of a car is loaded differently than the other end which poses different requirements for braking systems mounted at each truck.
Consequently, if uniform pressure is applied to the pneumatic means, i.e., the piston/cylinder, for the wheels of all the cars, the braking effect will be much higher on partially loaded and empty cars than on fully loaded cars. Obviously, as would be expected, this situation is undesirable.